Catheters and guidewires which are used for insertion through blood vessels, urethra, or body conduits require a low-friction surface for preventing injury or inflammation of mucous membranes and for facilitating the surgical procedures. Conventional catheters have been rendered slippery by either construction with low-friction materials such as Teflon.RTM. and polyethylene, or substrates coated with a layer of Teflon.RTM., silicone fluid, glycerin, or olive oil. These catheters are useful but not completely satisfactory because of either an inadequate retention of lubricity, or a lack of hydrophilicity. A variety of approaches have been undertaken in recent years to develop surfaces through either direct surface modification or the use of hydrogel coatings derived from different water soluble polymers (Y. L. Fan, POLYMER NEWS, March 1992, vol. 17,no. 3, pp 70-74). Poly(ethylene oxide) is one of the water-soluble polymers used for this purpose.
Poly(ethylene oxide) polymer is well known for its friction-reduction and blood-compatibility properties (R. L. Davidson, Handbook of Water-Soluble Gums and Resins, McGraw-Hill Book Co., New York, chapter; 19-1, 1980: M. Szycher, High Performance Biomaterials, Technomic Publishing Co., Lancaster, pp. 401-404, 1991).
Lambert in a series of U.S. Patents describes a two-step coating process to afford a lubricious coating by first applying an isocyanate coating and followed by a poly(ethylene oxide) coating (U.S. Pat. Nos. 4,585,666 and 4,459,317) and articles coated by his process (U.S. Pat. No. 4,487,808).
Elton describes a one-step coating process using a reactive coating mixture composed of an isocyanate, a polyol, and a poly(ethylene oxide) to cure the reactants and produce a urethane coating. A significant deficiency of the process is the limited time the mixed reactants can be stored after mixing due the high reactivity between an isocyanate and a polyol in the coating solution. A second deficiency of the process is the moderate lubricity of the urethane surface.
Rowland describes a coating with reduced friction produced from a structural plastic and a high molecular weight poly(ethylene oxide), U.S. Pat. No. 5,041,100. This process suffers from a lack of coating durability and uniformity. The poly(ethylene) oxide in the mixture may leach from the coating upon exposure to water resulting in a reduction in lubricity.
Notwithstanding the teachings of the above references, a need exists to provide a satisfactory one-step lubricious coating for medical devices.